The invention relates to polymeric windows used in polishing pads for polishing with optical endpoint detection equipment. For example, the polishing pads are particularly useful for polishing endpoint detection of at least one of magnetic, optical, and semiconductor substrates.
Typically, semiconductor manufacturers use endpoint detection in chemical mechanical polishing (CMP) processes. In each CMP process, a polishing pad in combination with a polishing solution, such as an abrasive-containing polishing slurry or an abrasive-free reactive liquid, removes excess material in a manner that planarizes or maintains flatness for receipt of a subsequent layer. The stacking of these layers combines in a manner that forms an integrated circuit. The fabrication of these semiconductor devices continues to become more complex due to requirements for devices with higher operating speeds, lower leakage currents and reduced power consumption. In terms of device architecture, this translates to finer feature geometries and increased numbers of metallization levels. These increasingly stringent device design requirements are driving the adoption of smaller and smaller line spacing with a corresponding increase in pattern density. The devices' smaller scale and increased complexity have led to greater demands on CMP consumables, such as polishing pads and polishing solutions. In addition, as integrated circuits' feature sizes decrease, CMP-induced defectivity, such as, scratching becomes a greater issue. Furthermore, integrated circuits' decreasing film thickness requires that semiconductor fabricators do not introduce defects through over-polishing.
Over-polishing between semiconductor layers can result in copper interconnect “dishing” and dielectric “erosion”. Dishing refers to the excessive metal removed from an interconnect—dished metal interconnects have a dish-shaped profile worn away during polishing. Dishing has the adverse effect of increasing resistance and excessive dishing can result in immediate or early device failure. Dielectric erosion refers to the general loss of dielectric that can occur during over-polishing. For example, dielectrics and especially low-k dielectrics have a tendency to wear when not protected by a hardmask. Over the last several years, manufacturers of silicon integrated circuits have been using endpoint detection to prevent excessive over-polishing.
Endpoint detection typically relies upon a signal such as a laser or light signal sent through a polymeric sheet, such as that described by John V. H. Roberts in U.S. Pat. No. 5,605,760 (Roberts '760) to provide an accurate polishing endpoint. Although the polyurethane window of the Roberts '760 pad is still in use today, it lacks the optical transmission required for demanding applications. Furthermore, when these windows are formed in situ by casting polyurethane polishing material around a solid polyurethane window, they can cause problems by bulging during polishing. Window bulging represents the window bending upward or outward from the polishing platen; and a bulging window presses against the semiconductor wafer with increased force to create a significant increase in polishing defects. A second generation window introduced in early 2009 contained a coefficient of thermal expansion or CTE where the window CTE matched the pad CTE. Although this window solved the bulge issue, it also lacked the optical transmission required for demanding polishing applications.
Aliphatic isocyanate-based polyurethane materials, such as those described in U.S. Pat. No. 6,984,163 provided improved light transmission over a broad light spectrum. Unfortunately, these aliphatic polyurethane windows tend to lack the requisite durability required for demanding polishing applications. There is a need for a polishing window that possesses high optical transmission, lacks outward window bulging and has the required durability for demanding polishing applications.